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Non‐pathogenic rhizosphere bacteria belonging to the genera R hizorhapis and S phingobium provide specific control of lettuce corky root disease caused by species of the same bacterial genera
Author(s) -
Bruggen A. H. C.,
Francis I. M.,
Jochimsen K. N.
Publication year - 2014
Publication title -
plant pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.928
H-Index - 85
eISSN - 1365-3059
pISSN - 0032-0862
DOI - 10.1111/ppa.12212
Subject(s) - biology , rhizosphere , bacteria , inoculation , biological pest control , pathogenic bacteria , botany , horticulture , microbiology and biotechnology , genetics
Lettuce corky root ( CR ) is caused by bacteria in the genera R hizorhapis , S phingobium , S phingopyxis and R hizorhabdus of the family Sphingomonadaceae. Members of this family are common rhizosphere bacteria, some pathogenic to lettuce. Sixty‐eight non‐pathogenic isolates of bacteria obtained from lettuce roots were tested for control of CR caused by R hizorhapis suberifaciens CA 1 T and FL 1, and S phingobium mellinum WI 4 T . In two initial screenings, 10 isolates significantly reduced CR induced by one or more pathogenic strains on lettuce seedlings in vermiculite, while seven non‐pathogenic isolates provided significant CR control in natural or sterilized field soil. R hizorhapis suberifaciens FL 11 was effective at controlling all pathogenic strains, but most effective against R . suberifaciens CA 1 T . The other selected isolates controlled only pathogenic strains belonging to their own genus. In a greenhouse experiment, a soil drench with selected biocontrol agents ( R . suberifaciens FL 11, S phingomonas sp. NY 3 and S . mellinum CA 16) controlled CR better than seed treatments or application of alginate pellets. In microplots infested with R . suberifaciens CA 1 T , seed treatment with R . suberifaciens FL 11 provided complete control and a soil drench with FL 11 significantly reduced the disease. Pathogenicity tests with FL 11 on 23 plant species in 10 families resulted in slight yellowing on roots of lettuce and close relatives; similar yellowing appeared on some roots of non‐inoculated lettuce plants. This research showed that biocontrol agents can be genus‐specific. Only one isolate, FL 11, provided more general control of various pathogenic strains causing CR even in field soil in pots and microplots.